System and method for protecting a vessel and vessel

ABSTRACT

A protective casing for a vessel includes an outer shell surrounding the vessel wall. A spacer extends from adjacent the vessel wall toward the outer shell and spaces the outer shell away from the vessel wall. The spacer permits substantially uninhibited deformation of the outer shell to failure inward toward the vessel wall when a missile impact is imparted on the outer shell such that the outer shell substantially dampens the transmission of the energy of the missile impact to the exterior vessel wall. The spacer can position the outer shell to allow reinforcing fibers of the outer shell to elongate to the yield point to maximize energy absorption. Embodiments of the protective casing and a protected vessel, as well as a kit and method for forming the protective casing, are disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No. 62/146,704, entitled SYSTEM AND METHOD FOR PROTECTING A VESSEL AND VESSEL, which was filed on Apr. 13, 2015 and is hereby incorporated by reference for all purposes.

FIELD

The present invention generally relates to protecting vessels against missile impacts, and more specifically to positioning an outer shell of deformable energy absorbing material around a vessel wall to absorb energy of a missile impact imparted thereupon.

BACKGROUND

Vessels that store materials (e.g., hazardous materials) are often located in regions where, due to the weather conditions in the region, they may be at risk of missile impacts. A missile impact occurs when a projectile moving at a high rate of speed impacts a vessel wall. Oftentimes, during a large storm, such as a tornado or hurricane, storm winds carry loose debris through the storm area at sufficiently high speeds to impart missile impacts on a vessel located in the storm area. The Nuclear Regulatory Commission defines several categories of missile objects capable of imparting a missile impact upon a vessel when traveling at missile velocities. Representative missile objects include a 6.625-inch (16.8275 cm) diameter schedule 40 steel pipe that is 15 feet (4.572 meters) in length, a full-sized automobile, and a one-inch (2.54 cm) diameter steel sphere. The Nuclear Regulatory Commission's design basis for tornado missiles assumes the steel pipe and automobile travel at missile velocities of 135 ft/s (41.148 m/sec), 112 ft/s (34.1376 m/sec), and 79 ft/s (24.0792 m/sec) and assumes that the solid steel sphere travels at missile velocities of 26 ft/s (7.9248 m/sec), 23 ft/s (7.0140 m/sec), and 20 ft/s (6.096 m/sec). Likewise the American Society for Testing and Materials defines several categories of missiles capable of imparting a missile impact upon a vessel. The American Society for Testing and Materials' “Missile Levels” include a two-gram (0.00440925 lb.) steel ball traveling at 130 ft/sec (39.624 m/sec) (Missile Level A), a two-pound (0.907185 kg) piece of lumber traveling at 50 ft/sec (15.24 m/s) (Missile Level B), a 4.5-pound (2.04117 kg) piece of lumber traveling at 40 ft/sec (12.192 m/sec) (Missile Level C), a nine-pound (4.08233 kg) piece of lumber traveling at 50 ft/sec (15.24 m/sec) (Missile Level D), and a nine-pound piece (4.08233 kg) of lumber traveling at 80 ft/sec (24.384 m/sec) (Missile Level A). Those skilled in the art will appreciate that the Missile Levels are merely exemplary of representative types of missiles and that missile impacts can be imparted by projectiles of various sizes and shapes traveling at various rates of speed.

Most vessels are not constructed to withstand missile impacts. When a missile impact is imparted on a vessel, the missile can perforate the vessel wall, thereby negating the vessel's ability to contain its contents. It is known to use concrete and steel barriers to protect vessels against missile impacts. However, these systems are costly, heavy, and difficult to install, and in some instances require additional regulatory involvement. Accordingly, an improved system and method for protecting a vessel against missile impacts is desired. Likewise, a vessel that is protected against perforation when a missile impact is imparted on the vessel is desired.

SUMMARY

In one aspect, a vessel is protected to inhibit the vessel from perforating when a missile impact is imparted on the vessel. The vessel comprises an exterior vessel wall. An outer shell surrounds the exterior vessel wall. The outer shell comprises an energy absorbing material deformable when the missile impact is imparted thereupon to absorb energy of the missile impact. A spacer extends from adjacent the exterior vessel wall toward the outer shell and spaces the outer shell away from the exterior vessel wall. The spacer is configured to permit substantially uninhibited deformation of the outer shell inward toward the vessel wall when the missile impact is imparted on the outer shell such that the outer shell substantially dampens the transmission of the energy of the missile impact to the exterior vessel wall.

In another aspect, a kit for protecting an exterior wall of a vessel to inhibit the vessel from perforating when a missile impact is imparted on the vessel comprises a spacer configured to be mounted on the exterior wall of the vessel and to extend away from the exterior wall a spacer thickness when mounted thereupon. An outer shell is configured to be mounted on the spacer when the spacer is mounted on the exterior wall of the vessel such that the spacer spaces the outer shell apart from the exterior wall by the spacer thickness. The outer shell comprises an energy absorbing material when mounted on the spacer. The energy absorbing material is deformable inward toward the vessel wall when the missile impact is imparted thereupon to absorb energy of the missile impact.

In another aspect, a method of protecting an exterior wall of a vessel to inhibit the vessel from perforating when a missile impact is imparted on the vessel comprises mounting a spacer on the exterior wall of the vessel and mounting an outer covering on the spacer such that the spacer spaces the outer covering from the exterior vessel wall. The outer covering forms an outer shell around the exterior wall when mounted on the spacer. The outer shell comprises an energy absorbing material that is deformable inward toward the vessel in response the missile impact being imparted thereupon to absorb energy of the missile impact.

Other aspects, features, and embodiments will be, in part, apparent and, in part, pointed out in this disclosure and the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective of a conventional storage tank;

FIG. 2 is a perspective of a protected tank;

FIG. 3 is a fragmentary horizontal section of the protected tank;

FIG. 4 is like FIG. 3, illustrating the protected tank after a missile impact is imparted to the tank; and

FIG. 5 is a magnified fragmentary perspective of a wall of the protected tank with layers broken away and illustrating reinforcing fiber bundles schematically with broken lines.

Corresponding reference characters indicate corresponding parts throughout the drawings.

DETAILED DESCRIPTION

Referring to FIG. 1, a conventional vessel for storing industrial liquid is generally designated by reference number 10. In the illustrated embodiment, the vessel 10 is a contaminated water storage tank with a steel exterior wall 12, such as may be used to store contaminated water at a nuclear power plant. The tank 10 is not constructed to withstand a missile impact, and when a missile impact is imparted upon the tank wall 12 the missile can perforate the wall, causing leakage or loss of the tank's contents. The tank 10 is merely exemplary of one type of vessel for which there is a need for protection against missile impacts. Other types of vessels for storing other types of materials can also be used without departing from the scope of the invention. A vessel that is protected against missile impacts according to the principles described below can have an exterior vessel wall of any suitable material and that is arranged to define any suitable vessel shape. As will be apparent to those skilled in the art, the present disclosure describes systems and methods for protecting vessels such as the tank 12 against missile impacts. Thus, aspects of the present disclosure can be implemented with the tank 10 or another type of unprotected vessel to construct a protected vessel that is protected against impacts imparted on the vessel by a projectile driven by, for example, storm winds during a tornado or other storm. It is also envisioned that the protection may be used on objects over than vessels.

Referring to FIG. 2, a protected contaminated water storage tank that is protected to withstand missile impacts is generally designated by reference number 110. The protected tank 110 includes the steel-walled tank 10, which is substantially sheathed in a protective casing, generally designated by reference number 112. As is evident from FIGS. 1 and 2, the protected tank 110 can be constructed from a tank 10 that is manufactured conventionally prior to installation of the protective casing 112. Thus, the protective casing may be applied to the steel wall 12 of the tank 10 as a retrofit addition to the tank in the field. Alternatively, the protective casing 112 may be applied to the steel wall 12 of the tank 10 as part of a tank 110 that is protected against missile impacts as originally manufactured. As shown in FIG. 3, the protective casing 112 includes, in the illustrated embodiment, an inner shell, generally designated by 114, a spacer generally designated by 116, and an outer shell generally designated by 118.

The inner shell 114 is bonded to and substantially covers the tank wall 12. Although the inner shell 114 is bonded to the tank wall 12, in other embodiments the inner shell can be secured to the tank wall in other ways (e.g., mechanical fasteners, etc.) without departing from the scope of the invention. The inner shell 114 is located between the tank wall 12 and outer shell 118 and surrounds the tank wall. The inner shell 114 is preferably made from a high-strength, energy absorbing material, such as fiber-reinforced polymer. The inner shell 114 is configured to absorb energy from a missile impact, thereby limiting the transmission of missile impact energy to the tank wall 12. As discussed in further detail below, the inner shell also provides a bonding surface for bonding the spacer 116 to the tank 10.

In the illustrated embodiment, the inner shell 114 comprises a single layer of unidirectional fiber-reinforced polymer. Unidirectional fiber-reinforced polymer has reinforcing fibers oriented substantially in a single direction. For example, a unidirectional fiber-reinforced polymer can include bundles of reinforcing fiber that are stitched together into a fabric and suspended within a polymer matrix. Unidirectional fiber-reinforced polymers have high tensile strength in a direction parallel to their reinforcing fibers.

As shown in FIG. 5, the illustrated unidirectional material includes fiber bundles 120 that form a fabric sheet suspended in a polymeric material. The fiber bundles 120 are arranged so that, when the fabric is wetted with a curable liquid, the fabric holds (e.g., is saturated with) the curable liquid. The reinforcing fiber bundles 120 are oriented parallel to one another. Each of the fiber bundles 120 extends circumferentially around the tank wall 12 in a horizontal direction. Although the illustrated embodiment uses unidirectional reinforcing fabric, other inner shell architectures (e.g., bi-directional, woven, braided, knit, or stitched) may also be used without departing from the scope of the invention. Moreover, the inner shell may include multiple layers and/or layers of material that are not “fabrics.” Preferably, each of the bundles 120 is made of one of glass fibers and carbon fibers. Other types of fiber materials (e.g., basalt, carbon, and aramid) may also be used without departing from the scope of the invention. The polymeric material can be an epoxy, a resin, or any other suitable material. However, in preferred embodiments, the polymer comprises a curable material. In one or more preferred embodiments, the inner shell 114 comprises Tyfo® SEH-51A unidirectional glass fiber suspended in a matrix of cured Tyfo® S Epoxy. In one or more additional embodiments, the inner shell 114 comprises, Tyfo® SCH-41 unidirectional carbon fiber suspended in a matrix of cured Tyfo ® S Epoxy.

The inner shell 114 may include multiple layers of unidirectional fiber-reinforced polymer, successively bonded to and covering the adjacent inner layer. Preferably, when multiple layers of unidirectional fiber-reinforced polymer are used to form the inner shell 114, the directional fiber bundles in adjacent layers are oriented transverse to one another, so that the directional strength characteristics of successive layers can be combined to enhance the overall strength of the inner shell. For example, the directional fiber bundles in a first layer of the inner shell 114 can be oriented at about 0° (e.g., substantially horizontally) and the directional fiber bundles in a second layer of the inner shell can be oriented at about 90°. Successive layers preferably alternate between directional fibers oriented at about 0° and about 90°. Each layer of the inner shell can, for example, have a thickness from about 0.01 inches (0.0254 cm) to about 0.10 inches (0.254 cm). In total, the inner shell can include from one layer to about 4 layers of unidirectional fiber-reinforced polymer.

The spacer 116 is bonded to the inner shell 114 and extends outward from adjacent the exterior tank wall 12 toward to outer shell 118 to space the outer shell away from the tank wall. As shown in FIG. 3, the spacer 116 extends outwardly a spacer thickness T from an inner end located adjacent the tank wall 12 to an outer end located adjacent an outer shell 118. The spacer thickness T is preferably from about 0.1 inches (0.254 cm) to about 5 inches (12.7 cm) and, more preferably, from about 0.5 inches (1.27 cm) to about 2 inches (5.08 cm). The spacer 116 is disposed between the inner shell 114 and outer shell 118. The spacer 116 comprises one or more sheets of pliable material wrapped around the perimeter of the tank wall 12. The spacer material is configured to bend to conform to the shape of the tank wall 12 while substantially retaining the spacer thickness T. As will be discussed in greater detail below, the spacer 12 is preferably configured to space the outer shell 118 apart from the tank wall 12 so that the outer shell can deform inward in response to a missile impact. Thus, the spacer 116 is configured for compressive deformation when a missile impact is imparted upon the reinforced vessel 110. Various materials can be used for the spacer 116, including plastic, aluminum, foam, paper, fiber-reinforced composite, or any other suitable material.

Referring to FIG. 5, the spacer 116 preferably comprises a cellular formation oriented transverse to the tank wall 12 and surrounding the tank wall. The cellular formation defines a plurality of honeycomb cells 122 extending between the tank wall 12 and the outer shell 118. In the illustrated embodiment, the cells 120 are defined by alternating walls of flat and corrugated material that are joined together along axially extending joints. Other cellular architectures can also be used without departing from the scope of the invention. In a preferred embodiment, the cellular formation 116 comprises paper. The paper cellular formation 116 is inexpensive to manufacture and can be bent to conform to the shape of a vessel 10, while being robust enough to support the outer shell 118 in spaced apart relation with the tank wall 12. In addition, paper cellular formation 116 readily deforms when energy of a missile impact is imparted thereupon. In some embodiments, where it is desirable for the spacer to absorb a significant portion of the energy of the missile impact, it may be preferable to use a cellular formation comprising a higher strength material (e.g., plastic, aluminum, fiber-reinforced polymer, etc.). But the spacer should preferably not be so strong that it substantially inhibits the outer shell from deforming inward. It is envisioned that deformable spacers having other than a honeycomb structure may be used.

Referring again to FIG. 3, the spacer 116 is anchored to the tank wall 12 using one or more anchors 124. In the illustrated embodiment, the anchors 124 include threaded dowels that are threadably received in the tank wall 12. It will also be understood that the dowels can be attached to the tank wall 12 by an adhesive material, welding, or other methods of attachment. These attachment methods may be preferable to coring and tapping threaded openings in the tank wall for threadably receiving the dowels therein. Free ends of the dowels 124 extend outward from the tank wall 12 to form radially extending lugs for anchoring the spacer 116 to the tank wall. The spacer 116 is installed on the tank wall 12 so that the lugs 124 extend into the honeycomb cells 122 and engage the honeycomb formation, thereby inhibiting the spacer from shifting in position relative to the tank wall. Other anchoring mechanisms can also be used, or an anchoring system may be omitted altogether, without departing from the scope of the invention.

The outer shell 118 surrounds the tank wall 12 and is spaced away from the tank wall by the spacer 116. The outer shell 118 is preferably bonded to the spacer 116 to form the protective casing 112, although the outer shell can be mounted on the spacer in other ways without departing from the scope of the invention. The outer shell 118 comprises energy absorbing material that is deformable when a missile impact is imparted thereupon. In a preferred embodiment, the outer shell 118 comprises a fiber-reinforced polymer material. As will be discussed in further detail below, the fiber-reinforced polymer is capable of absorbing energy of a missile impact imparted thereupon to protect the tank 10 from perforating when a missile impact is imparted on the protected tank 110.

In the illustrated embodiment, the outer shell 118 comprises two layers 118A, 1186 of unidirectional fiber-reinforced polymer. As shown in FIG. 5, the inner layer 118A comprises bundles of reinforcing fibers 130 (e.g., carbon, glass, basalt, or aramid fibers) oriented vertically and extending parallel to a vertical axis of the tank 110, and the outer layer 1186 comprises bundles of reinforcing fibers 132 oriented horizontally and extending circumferentially around the tank 10. Preferably, the bundles 130, 132 comprise reinforcing fibers that have a high tensile strength and are at least somewhat ductile so that when a missile impact is imparted upon the shell the reinforcing fibers absorb impact energy through elongation prior to failure. Although the illustrated outer shell 118 includes inner and outer layers 118A, 1186 with unidirectional reinforcing fibers oriented perpendicular to one another, in other embodiments the reinforcing fibers of adjacent layers of unidirectional fiber-reinforced polymer can be oriented at other transverse angles without departing from the scope of the invention. In addition, the orientation of the reinforcing fiber bundles 130, 132 in the inner and outer layers 118A, 118B could be reversed or otherwise reoriented without departing from the scope of the invention.

Preferably, each set of reinforcing bundles 130, 132 is arranged in a sheet of fabric adapted to carry (e.g., be saturated with) a curable polymeric material. Likewise the fiber bundles 130, 132 are preferably suspended in a polymeric material that is curable. In one or more preferred embodiments, each of the outer shell layers 118A, 118B comprises Tyfo® SEH-51A unidirectional glass fiber fabric suspended in a matrix of cured Tyfo® S Epoxy. In one or more additional embodiments each of the outer shell layers 118A, 118B comprises Tyfo® SCH-41 unidirectional carbon fiber suspended in a matrix of cured Tyfo® S Epoxy.

Additional layers (not shown) of unidirectional fiber-reinforced polymer can also be added to the outer shell 118 to increase the strength of the outer shell. The layering of unidirectional fiber-reinforced polymer layers enables strength to be added to the outer shell in discrete amounts, one layer at time. Thus, a user can optimize the strength characteristics of the protective casing 112 without wasting material. In one or more embodiments, each additional layer is bonded to the adjacent inner layer. The reinforcing fibers in one layer are preferably oriented transverse to the reinforcing fibers in the adjacent inner layer and an adjacent outer layer bonded thereto. In certain embodiments, successive layers alternate between having reinforcing fibers oriented in a first direction (e.g., horizontally) and having reinforcing fibers oriented in a second direction (e.g., vertically), transverse (e.g., perpendicular) to the first direction. As discussed above, unidirectional fiber-reinforced polymer is known to have high tensile strength in the direction parallel to the orientation of its reinforcing fibers. By orienting successive layers in transverse directions, the overall strength of the outer shell is improved since the layers impart strength in different directions. Each layer of unidirectional fiber-reinforced polymer in the outer layer can, for example, have a nominal thickness of from about 0.01 inches (0.0254 cm) to about 0.05 inches (0.127 cm). In total, the outer shell 118 can, for example, comprise from about 1 to about 8 layers.

Although the illustrated embodiment of the protected tank 110 uses two layers 118A, 118B of unidirectional fiber-reinforced polymer to form the outer shell 118, it will be understood that the outer shell could be formed from other materials without departing from the scope of the invention. For example, it is contemplated that the outer shell 118 could be formed from a single layer of fiber-reinforced polymer, with any suitable fiber architecture (e.g., bi-directional, woven, braided, knit, or stitched). It is also contemplated that other materials besides fiber-reinforced polymer could be used for the outer shell without departing from the scope of the invention.

In a preferred embodiment the outer shell 118 is configured to absorb significantly more of the energy of a missile impact than the spacer 116. As discussed above, the outer shell 118 preferably comprises reinforcing fibers having high tensile strength and some ductility (e.g., less ductility than the steel tank wall 12, but enough ductility to permit elongation of the reinforcing fibers when a missile impact is imparted to the outer shell). As a result, when a missile impact is imparted upon the outer shell 118 and causes deformation of the outer shell, the reinforcing fibers absorb a significant amount of impact energy as they deform longitudinally prior to failing. By comparison, in the illustrated embodiment the spacer 116 is a paper cellular formation with relatively low compressive strength. As shown in FIG. 4, in a preferred embodiment, the spacer 116 spaces the outer shell 118 apart from the tank wall 12 a sufficient distance to permit the outer shell to deform to failure prior to engaging the tank wall. The missile impact causes lengthwise deformation of the reinforcing fibers that exceeds the tensile strength of the fibers and causes them to fracture or otherwise fail. However, the deformation and fracturing of the reinforcing fibers absorbs a significant amount of the energy of the missile impact such that the missile impact does not perforate the tank 110. In some cases, the missile impact may cause deformation (e.g., denting) of the tank wall 12 without causing perforation. The denting of the tank wall 12 will also absorb a portion of the missile impact energy.

In one or more embodiments, the protected tank 110 is configured so that the tank wall 12 is not perforated when the protected tank is subjected to a missile impact. For example, the outer shell 118 is configured to absorb enough of the kinetic energy of the missile impact so that the tank wall 10 has sufficient strength to absorb any additional kinetic energy of the missile impact without perforation. Where a protected vessel 110 is to be designed to withstand a predetermined missile impact having a total kinetic energy of E_(K), the outer shell 118 is preferably configured to absorb energy E_(S) that is greater than the difference between the total kinetic energy of the missile impact and the critical kinetic energy E_(T) of the tank wall 12 (i.e., E_(S)>E_(K)−E_(T)). The critical kinetic energy E_(T) of the tank wall is the maximum kinetic energy the tank wall can absorb before being perforated.

Using the critical kinetic energy E_(T) of the tank wall 12, a minimum energy absorption E_(S(min)) of the outer shell 118 can be determined from Equation 1.

E _(S(min)) =E _(K) −E _(T)   (1)

In order for the outer shell 118 to be capable of absorbing kinetic energy equal to its critical energy E_(S), the fibers 130, 132 in the outer shell must be spaced apart from the tank wall 12 as sufficient distance to allow elongation to tensile failure. Thus, the protective covering 112 can be designed to prevent the tank 10 from perforating when impacted by a missile impact having a kinetic energy E_(K) when two design criteria are met: (1) the number of reinforcing layers used forms an outer shell 118 having a thickness great enough to absorb E_(S(min)) and, (2) the outer shell material is spaced apart from the tank wall 12 a sufficient distance to allow the fiber reinforcement 130, 132 to elongate to failure. One skilled in the art will appreciate that the thickness of the spacer material 116 may be determined based on the elongation at failure of the reinforcing fibers 130, 132 to satisfy the second design criteria.

Compressive deformation of the cellular formation 116 absorbs relatively little impact energy in comparison to the deformation of the outer shell 118. For example, in one or more embodiments, deformation of the outer shell 118 is configured to absorb from about 85% to about 95% of the energy of the missile impact, whereas deformation of the cellular formation is configured to absorb from about 5% to about 15% of the energy of the missile impact. Likewise, the outer shell can be configured to absorb at least about nine-times as much of the energy of the missile impact as the deformation of the cellular formation.

For particularly high risk or high value applications, a protected vessel can comprise more than one protective casing 112. A second spacer (not shown) is bonded to or otherwise mounted on the outermost layer 1186 of the outer shell 118, and a second outer shell (not shown) is bonded to or otherwise mounted on the second spacer. Additional spacers and outer shells can also be added as needed to achieve the desired protection. Each additional protective casing 112 adds greater protection against missile impact because each successive outer shell is spaced apart by a spacer, which enables each outer shell to absorb impact energy as it deforms inward into the space occupied by the spacer.

In one embodiment, the protected tank 110 is manufactured from a kit that includes unidirectional fiber fabric, a pliable cellular formation (e.g., a sheet of cellular material), and a curable epoxy. The fiber fabric is configured to be cut into a first sheet sized to substantially cover the exterior wall 12 of the tank. The first sheet is adapted to be saturated with the curable epoxy, applied to the tank wall 12, and cured to form the inner shell 112. In one or more embodiments, the kit includes additional fiber fabric sheets configured to be saturated with epoxy and bonded to the first fabric sheet to form a multi-layer inner shell. The cellular formation is configured to be mounted on the tank to form the spacer 114. Preferably, the cellular formation bends to conform to the shape of the tank 12 when mounted on the tank. In certain embodiments, the kit comprises threaded anchoring dowels 124 configured to be installed in the tank wall 12 and positioned within the cells 122 of the spacer 114 to position the spacer on the tank wall 12. The unidirectional fiber fabric is further configured to be cut into second and third sheets sized to substantially cover the spacer 114. The second sheet is adapted to be saturated with the curable epoxy, applied to the outer end of the spacer 114 with its reinforcing fibers oriented in a first fiber direction, and allowed to cure, thereby forming the inner layer 118A of the outer shell 118. The third sheet is adapted to be saturated with the curable epoxy, applied to the inner layer 118A of the outer shell 118 so that the reinforcing fibers are oriented transverse (e.g., perpendicular to) the reinforcing fibers in the inner layer, and allowed to cure, thereby forming the outer layer 1186. Additional sheets may also be included in the kit to create an outer shell of more than two layers.

In one method of protecting a tank 10 against missile impacts, the inner shell 114 is installed on the tank by saturating at least a first sheet of unidirectional fiber fabric with a curable epoxy, applying the saturated fabric to the wall 12 of the tank, and allowing the fabric to cure. The first sheet is installed as an inner covering on the tank that, when cured, forms the inner shell 114. A spacer 116 is mounted on the tank 10 by bending a cellular formation with a spacer thickness T to conform to the shape of the tank while the epoxy in the inner shell is curing, thereby bonding the spacer material to the inner shell 112. In certain embodiments, threaded dowels 124 are received in the cells 124 to position the cellular formation on the tank wall 12. An outer shell 118 is installed by saturating a second sheet of unidirectional fiber fabric with a curable epoxy, applying the second sheet as a covering over the spacer with the reinforcing fibers in the fabric oriented in a first direction, and allowing the second sheet to cure. A third sheet of unidirectional fiber fabric is saturated with curable epoxy, applied as a covering over the second sheet with the reinforcing fibers in the third sheet oriented transverse to the reinforcing fibers in the second sheet, and allowed to cure. Together, the second and third sheets are installed as an outer covering on the spacer that, when cured, forms the outer shell 118.

Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 

What is claimed is:
 1. A vessel protected to inhibit the vessel from perforating when a missile impact is imparted on the vessel, the vessel comprising; an exterior vessel wall; an outer shell surrounding the exterior vessel wall, the outer shell comprising an energy absorbing material deformable when the missile impact is imparted thereupon to absorb energy of the missile impact; a spacer extending from adjacent the exterior vessel wall toward the outer shell and spacing the outer shell away from the exterior vessel wall, the spacer being configured to permit substantially uninhibited deformation of the outer shell inward toward the vessel wall when the missile impact is imparted on the outer shell such that the outer shell substantially dampens the transmission of the energy of the missile impact to the exterior vessel wall.
 2. A vessel as set forth in claim 1 wherein the spacer is configured to permit the outer shell to deform to failure prior to engaging the exterior vessel wall.
 3. A vessel as set forth in claim 2 wherein the spacer comprises a cellular formation oriented transverse to the vessel wall and extending from an inner end located adjacent the vessel wall to an outer end located adjacent the outer shell.
 4. A vessel as set forth in claim 3 wherein the cellular formation defines a plurality of honeycomb cells extending axially between the vessel wall and the outer shell.
 5. A vessel as set forth in claim 4 wherein the cellular formation surrounds the vessel wall.
 6. A vessel as set forth in claim 3 further comprising at least one anchor anchoring the cellular formation to the vessel wall.
 7. A vessel as set forth in claim 6 wherein the anchor comprises a dowel have a threaded end threadably received in the vessel wall and a free end secured to the cellular formation.
 8. A vessel as set forth in claim 3 wherein the cellular formation is configured to compressively deform when the outer shell deforms inward toward the exterior wall in response to the missile impact.
 9. A vessel as set forth in claim 1 wherein the deformation of the outer shell is configured to absorb from about 85% to about 95% of the energy of the missile impact and wherein the spacer is configured to absorb from about 5% to about 15% of the energy of the missile impact.
 10. A vessel as set forth in claim 8 wherein the deformation of the outer shell is configured to absorb at least about nine-times as much of the energy of the missile impact as the deformation of the spacer.
 11. A vessel as set forth in claim 3 wherein the cellular formation comprises paper.
 12. A vessel as set forth in claim 1 further comprising an inner shell surrounding the vessel wall and located between the vessel wall and the outer shell.
 13. A vessel as set forth in claim 12 wherein the spacer is disposed between the inner shell and the outer shell.
 14. A vessel as set forth in claim 12 wherein the inner shell is bonded to the vessel wall.
 15. A vessel as set forth in claim 12 wherein the inner shell comprises fiber-reinforced polymer.
 16. A vessel as set forth in claim 1 wherein the outer shell comprises fiber-reinforced polymer.
 17. A vessel as set forth in claim 16 wherein the outer shell comprises a first layer of fiber-reinforced polymer having fibers oriented substantially in a first direction and a second layer of fiber-reinforced polymer having fibers oriented substantially in a second direction transverse to the first direction.
 18. A vessel as set forth in claim 16 wherein the fiber-reinforced polymer comprises glass fibers and resin.
 19. A kit for protecting an exterior wall of a vessel to inhibit the vessel from perforating when a missile impact is imparted on the vessel, the kit comprising: a spacer configured to be mounted on the exterior wall of the vessel and to extend away from the exterior wall a spacer thickness when mounted thereupon; and an outer shell configured to be mounted on the spacer when the spacer is mounted on the exterior wall of the vessel such that the spacer spaces the outer shell apart from the exterior wall by the spacer thickness, the outer shell comprising an energy absorbing material when mounted on the spacer, the energy absorbing material being deformable inward toward the vessel wall when the missile impact is imparted thereupon to absorb energy of the missile impact.
 20. A method of protecting an exterior wall of a vessel to inhibit the vessel from perforating when a missile impact is imparted on the vessel, the method comprising: mounting a spacer on the exterior wall of the vessel; and mounting an outer covering on the spacer such that the spacer spaces the outer covering from the exterior vessel wall, the outer covering forming an outer shell around the exterior wall when mounted on the spacer, the outer shell comprising an energy absorbing material that is deformable inward toward the vessel in response the missile impact being imparted thereupon to absorb energy of the missile impact. 